New research: exercise supports vitamin D in winter

If you follow the Overcoming MS Program, you know that maintaining healthy vitamin D levels is essential for people with MS, and experts increasingly agree on its importance. Now, a new study from the University of Bath brings some encouraging news. The VitaDEx study, published in May 2025, shows that regular exercise may help preserve levels of active vitamin D during the winter. For the Overcoming MS community, this adds another reason for why movement matters.

What did the VitaDEx study do?

Researchers recruited 51 inactive adults with a BMI in the overweight or obese range (25-35) and split them into two groups: 

• Exercise group: took part in four indoor cardio sessions per week (around 2.5 hours total) for 10 weeks over winter. 

• Control group: continued their usual (mostly inactive) lifestyle.

Importantly, nobody lost weight during the trial,  they were asked to maintain their weight so the effect of exercise alone could be tested. No participants took vitamin D supplements, and all sessions were indoors to rule out sun exposure.

Researchers measured levels of both stored vitamin D and the active form along with markers in blood and fat tissue. 

Key findings

Here’s what the research found: 

• The exercise group maintained their active vitamin D levels throughout the winter. 
• The control group experienced a 15% drop in active vitamin D levels over the same period. 
• There was also a moderate reduction in the seasonal drop of stored vitamin D in the exercise group, though not statistically significant. 
• The benefits may come from stimulating vitamin D metabolism, rather than simply releasing vitamin D from fat stores. 

This is the first well-conducted study to demonstrate that regular exercise, independent of weight loss or supplementation, may help maintain active vitamin D levels during winter. 

What does this mean for people with MS?

For those living with MS, this study supports what we already believe: movement is powerful. Not just for strength, mental health or fatigue management, but now potentially as a way to support vitamin D levels in winter. 

Here’s why it matters: 

• The active form of vitamin D (D3) is key for immune and nervous system health, and it’s this form that was maintained by exercise in the study. 
• Even without losing weight, moderate-intensity activity appears to support better vitamin D metabolism. 
• This complements, rather than replaces, other approaches like sun exposure in summer, healthy eating, and vitamin D supplements. 

It’s also worth noting that the participants in this study exercised about 2.5 hours a week, in line with UK and WHO guidelines – an achievable target for many people when adapted to their ability and energy levels. 

Practical takeaways

• Keep moving, especially in winter: Even a few moderate sessions per week may help protect your vitamin D status. 
• Don’t worry about weight loss: The benefits in this study were seen without any reduction in body weight. 
• Focus on consistency: The effect seems to come from regular, ongoing activity, not one-off workouts. 
• Think cardio, not just strength: This study used walking and cycling-based cardio workouts, but any activity that gets your heart rate up counts. 
• Work with your body: Always choose exercise types and intensities that feel manageable and safe for you. 

A final thought

Overcoming MS advises testing your vitamin D levels where possible, to develop a personalised supplementation plan. If this is not possible, we recommend supplementing with between 4,000 and 10,000 units of vitamin D daily, a safe and evidence-based approach.  

The VitaDEx study adds an exciting piece to the puzzle of how exercise benefits our health, particularly in winter, and particularly for people with MS. This research shows that exercise itself can influence how your body processes and maintains vitamin D. And that’s something you can do, whatever your starting point. 

Looking for support with movement?

Explore the free Overcoming MS exercise resources, including on-demand videos, expert-led classes, and our 6 months to Overcoming MS course to help you stay active in a way that works for you – all year round. 

Read the full VitaDEx study here: Exercise without Weight Loss Prevents Seasonal Decline in Vitamin D Metabolites: The VitaDEx Randomized Controlled Trial – Perkin – 2025 – Advanced Science – Wiley Online Library